Ms Le Pen said then that she had no intention of complying, and as a European member of parliament police cannot force her into questioning.

She has repeatedly claimed that she is a victim of a politically-motivated vendetta.

The BBC's Paris correspondent, Hugh Schofield, said Ms Le Pen's enemies hope the scandal will damage her reputation, but so far there is little sign of that, partly because there is no allegation of personal enrichment in the affair.

Ms Le Pen is one of the front-runners in the French presidential election to be held in April and May. If she wins, she has promised a Brexit-style referendum on France's membership of the EU.

Polls suggest that she will make it to the run-off where she is likely to face conservative candidate Francois Fillon or centrist Emmanuel Macron.